Question

calcule a soma dos 17 primeiros termos da P.A (49,41,33)

Answer 1

r= 41-49=-8

an=a1+(n-1).r

a17=49+(17-1).-8

a17=49+16.(-8)

a17=49-128=-79

soma= Sn= (a1 + an ).n/2

Sn= (49 +(-79).17/2=(49-79).17/2=-30.17/2= -510/2= -255